A study set to be released Wednesday determined Muhammad Ali displayed signs of slowed or slurred speech as much as a decade before he was diagnosed with Parkinson's disease.

According to ESPN.com's William Weinbaum, Arizona State University speech scientists Visar Berisha and Julie Liss studied public speaking appearances Ali made from 1968 through 1981 and found his speaking rate slowed by 26 percent from the ages of 26 to 39.

Ali was diagnosed with Parkinson's disease at the age of 42 and died in 2016 at the age of 74.

Jonathan Eig, author of the upcoming biographyAli: A Lifewas part of the study as well, and he found Ali's speech slowed by 16 percent after a 1977 fight against Earnie Shavers that saw him absorb 266 punches.

Eig concluded Ali's speech would slowly rebound the further removed he got from fights but that irreparable damage was done.

Per Weinbam, Eig said Ali had some knowledge regarding the danger he put himself in by fighting until he was nearly 40: "Ali did damage to himself and he knew it and kept boxing too long, but he didn't have the information we now have about CTE (chronic traumatic encephalopathy)—you don't have to wait until you're middle-aged to stop."

Ali's last fight was in 1981 against Trevor Berbick, and the study found he was already slurring his words three years prior to that.

The official Parkinson's diagnosis came almost three years after Ali retired from boxing.